In a cellular-based wireless communication system, a mobile station (MS) performs a handover whenever moving from one cell to another, thereby maintaining seamless communication while moving. That is, the mobile station measures channel states with respect to a serving base station (BS) and a neighboring base station, and, if the neighboring BS provides a superior channel state to the serving base station, performs a handover to the neighboring base station. It is desirable in this case that the handover is performed at a moment when the channel state (i.e., a received signal strength) of the neighboring base station becomes greater than a received signal strength of the serving base station. However, when the mobile station is located in a cell boundary area, the received signal strength of the serving base station may temporarily decrease under the influence of channel fading or interference. Therefore, if the handover is performed at a moment when the received signal strengths of the two base stations become equal to each other, at a similar time, the mobile station may perform a handover again. This phenomenon is referred to as a ping-pong effect.
In order to reduce the ping-pong effect, the mobile station uses a hysteresis value (i.e., threshold) in a process of comparing received signal strengths. That is, the mobile station performs a handover at a time when a difference between the received signal strength of the neighboring base station and the received signal strength of the serving base station reaches the hysteresis value. In general, the hysteresis value is a fixed value.
As described above, in a broadband wireless communication system, a mobile station performs a handover by using a fixed hysteresis value. The use of the hysteresis value results in the decrease in the ping-pong effect, but produces a handover delay. In particular, communication is disrupted due to the handover delay when the mobile station moves fast. In addition, there is a problem in that an overall system capacity decreases since communication is continued with a serving base station having a relatively low received signal strength. Therefore, there is a need for a method for controlling a hysteresis according to an environment of a mobile station.